1. Field of the Invention
The present invention relates to a thin film type magnetic recording medium and more particularly to a thin film type magnetic recording medium with an improved abrasion resistance and corrosion resistance.
2. Prior Art and its Drawback
The manufacturing method of a magnetic recording medium may roughly be classified into two categories from the viewpoint of a forming method of a magnetic layer; one is a coating method and the other is a method of evaporation or of plating.
In the magnetic recording medium prepared by the coating method (hereafter, a magnetic recording medium prepared by the coating method is referred to as "a coating type magnetic recording medium"), ferromagnetic powder such as .gamma.-Fe.sub.2 O.sub.3, Fe or the like is mixed with optimum binder resin and magnetic paint obtained after dispersion is coated on a non-magnetic substrate and then the processes such as magnetic orientation, drying, super-calendering and others are conducted thereon, thus the characteristics as a magnetic recording medium are obtained.
Even the coating type magnetic recording medium naturally requires a high coercive force, an improvement of the recording density, a thin film of magnetic layer and others. However, the method wherein the magnetic paint obtained by mixing ferromagnetic powder with binder is coated on a non-magnetic substrate has essentially the limit in the substantial containing rate of ferromagnetic powder and thus it has difficultly for aiming the high recording density and thin film.
For aforesaid reasons, there have been employed generally two methods for the aim of high recording density and thin film; one method is to cause magnetic materials to evaporate with a method such as vacuum deposition, sputtering, ion plating or the like so that the magnetic materials form a continuous thin film on a non-magnetic substrate and the other method is to form through an electrolytic method or a chemical plating (hereafter, a magnetic recording medium obtained through aforesaid methods is referred to as "a thin film type magnetic recording medium"). In the thin film type magnetic recording medium, it is possible to obtain the one having a high recording density characteristic in the short wavelength zone such as high density and thin film etc. which is not owned by aforesaid coating type magnetic recording medium.
However, the thin film type magnetic recording medium generally requires an improvement both in physical and chemical characteristics such as corrosion resistivity, abrasion resistance or the like and in an electromagnetic characteristic thereof.
For the improvement in physical and chemical characteristics of the thin film type magnetic recording medium prepared through aforesaid vacuum deposition, sputtering or ion plating etc., there have been proposed various methods. For example, (1) an over coat layer of abrasion proof metal is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 23704/1976, 47401/1976, 7205/1978, 39708/1978, 73108/1978 and 141107/1979, (2) an over coat layer of metallic oxide, metallic nitride or of metallic carbide being disclosed in Japanese Patent Publication Open to Public Inspection Nos. 4805/1977, 127204/1977 and 138054/1982, (3) an over coat layer of inorganic lubricant being disclosed in Japanese Patent Publication Open to Public Inspection Nos. 146302/1975 and 57002/1978 and (4) the one wherein an organic polymer superficial film is formed is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 153707/1977, 153534/1981, 8927/1982, 130436/1983 and 150128/1983. Further, (5) the one wherein organic lubricant such as fatty acid or esters of higher alcohol is coated or adsorbed is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 93533/1980 and 19736/1983 and further, (6) the one wherein an oxide film or a nitride film is formed through oxidation or nitriding on the surface of a magnetic layer is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 33806/1975, 153407/1977, 143111/1979, 15011/1981 and 26321/1983.
In the aforesaid prior arts, however, (1), (2), (3) and (4) require the film thickness of 0.1 .mu.m or more for the good effect on both corrosion resistance and abrasion resistance and such film thickness disables to obtain a sufficient capability as a high density recording medium due to the spacing loss produced therein. Further, due to the film formed additionally, the adhesive force between the magnetic layer and the film is insufficient, which causes the exfoliation between layers to take place easily, thus the abrasion resistance is especially problematic. Further in (5), the lubricant film easily comes off and easily be worn away therefore the characteristics such as the durability for the still and others have not been sufficient. Further in (6), the method is not suitable for the magnetic recording medium for video which employs a plastic substrate such as polyester or the like because the temperature goes up in the manufacturing stage owing to its method wherein oxidation and nitriding are performed with heat or kinetic energy of particles being added. Further in the wet system method wherein a solution reaction is employed, if a film having the practical characteristic is prepared, the thickness of the film tends to be thick that results in a spacing loss and if the film thickness is thin, on the contrary, the sufficient abrasion resistance can not be obtained and at the same time, the secondary problem such as the acceleration of corrosion or the like has been produced.